This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A systematic analysis of sequence variation and structural similarity in viral capsid proteins (VCPs) of non-enveloped, spherical viruses was explored. Intra family analysis of 95 coat protein subunits from 9 virus families suggest that remarkably the VCPs from the same family display greater degree of structural similarity with RMSDs ranging from 0 [unreadable]3 [unreadable] in spite of broad sequence variation (0-97%). This clearly points to the conservation of core structure among VCPs within each family. Furthermore, we analyzed the conservation of amino acids in terms of core, interface and surface lying residues. Not surprisingly, the solvent accessible (surface) residues are less conserved compared to solvent inaccessible (core and interface) residues. Even though, grouping of viruses into plant and non-plant virus families showed similar pattern of sequence conservation, the plant viruses appear to have relatively less variation in the sequence of surface exposed residues compared to non-plant viruses.